. Changes in histone variants, histone modifications as well as DNA methylation are often referred to as epigenetic regulation.
However, such changes may or may not be truly epigenetic in nature because common epigenetics definition requires mitotic or meiotic heritability (Chinnusamy and Zhu 2009). H2A.Z is a conserved variant of histone H2A that has been implicated in different processes, such as transcriptional regulation, telomeric silencing, genome stability, cell cycle progression, DNA repair, and recombination (Sura, Kabza et al. 2017).
Histone modification and ATP-dependent chromatin remodelling regulate chromatin structure to balance chromatin packaging and transcriptional access (Qin, Zhao et al. 2014). H2A.Z affects many processes in fungi and animals, including gene expression, recombination, and DNA repair (Xu, Leichty et al.
2018) H2A.Z is highly enriched at the transcription start site (TSS) of a large set of genes across cell types, consistent with a role in the regulation of transcription, Genome-wide studies in yeast have shown that H2A.Z enrichment at promoter-distal nucleosomes is required for initiation of transcription, while being inversely correlated with transcript levels (Sura, Kabza et al.
2017). Eukaryotic genomes possess several histone variants, and each of them confers different properties to the nucleosome, which in turn affects numerous biological processes, most commonly transcription. Histones can also be modified post translationally and in turn affect transcription (Dai, Bai et al. 2017).